Influence of Phenolic Acids upon Ion Uptake

The influence of 12 naturally occurring phenolic acids on the uptake of potassium by barley (Hordeum vulgare L. cv. Karlsberg) was examined using 86Rb-labelled potassium solutions. Without exception, all compounds tested, including both cinnamic acid and benzoic acid derivatives, caused a significant reduction of uptake. In addition, the inhibitory capacities of 15 variously substituted benzoic acids were determined over a range of different concentrations of inhibitors. For each of these compounds an inhibition constant (Ki), defined as the concentration required to produce a 50 per cent reduction of uptake, was determined. The Ki values were found to be strongly correlated with the octanol-water partition coefficients of the compounds under examination. It is clear from this study and previous work upon phosphate uptake that phenolic acids exert a generalized inhibitory effect upon active ion-uptake which is almost certainly mediated through reversible alterations in membrane permeability.